Generally it is easy for global mnc exp to move into singtel or any other local co but very hard the other way round. For e.g. if you are a singtel manager go and apply as analyst in google maybe still got 10% chance, if want to lateral transfer to become manager in Google is almost impossible. Staff from the 3 local telcos tend to play musical chairs with each other and sometimes within other glcs, but very rare do they succeed in moving outside the system into mnc. Those who do so are usually younger staff within 2-3 years after graduating.